Various methods, sealants and tire constructions have been suggested for pneumatic tires that relate to use of liquid sealant coatings in which the sealant flows into the puncture hole. However, such liquid sealants can flow excessively at elevated temperatures and cause the tire to become out of balance. Also, the liquid sealant may not be entirely operable or effective over a wide temperature range extending from summer to winter conditions. More complicated tire structures which encase a liquid sealant in a vulcanized rubber material can be expensive to manufacture and can also create balance and suspension problems due to the additional weight required in the tire.
Puncture sealing tires also have been further proposed wherein a sealant layer of degradable rubber is assembled into an unvulcanized tire to provide a built-in sealant. The method of construction, however, is generally only reasonably possible when, for example, the sealant layer is laminated with another non-degraded layer of rubber, e.g., a tire inner liner, which permits handling during the tire building procedure. This is because the degradable rubber tends to be tacky or sticky in nature and lacks strength making it very difficult to handle alone without additional support. The inner liner also keeps the sealant layer from sticking to a tire-building apparatus. By laminating the sealant layer between two or more non-degraded rubber layers, e.g., the tire inner liner and a tire carcass, the sealant layer retains structural integrity during the vulcanization operation wherein high pressures are applied to the tire, which would otherwise displace the degraded rubber layer from its desired location. Accordingly, the resulting puncture sealing tire typically has a sealant layer between the inner liner and tire carcass.
Such a lamination procedure significantly increases the cost of manufacturing a tire. In addition, the compounds in the built-in sealant, e.g., organic peroxide depolymerized butyl rubber, may generate gases at higher temperature, such as during cure or during tire use, which can result in aesthetically unappealing inner liner blister formation. Aside from being unappealing, such blister formation may allow the sealant to unfavorably migrate away from its intended location. To combat blister formation, the inner liner, for example, can be provided at an increased thickness but this can add to the cost of building a tire. In addition, increased thickness may undesirably increase heat generation during tire use.
Accordingly, there is a need for a simple and practical method of preparing a self-sealing tire that eliminates or reduces blister formation in the tire inner liner.